The present invention relates in general to motor vehicle headlights.
Conventionally, a headlight comprises a filament lamp or an arc lamp having its source placed in the region of the focus of a mirror which can be a paraboloid of revolution or any other surface suitable for producing a beam of desired photometric characteristics, possibly in combination with optical arrangements provided on a glass.
For many years there has been a trend, particularly with improvements to bodywork in terms of aerodynamics, towards headlights being made that are small in height, with a reflecting surface that is truncated by a top cheek and a bottom cheek. To prevent these cheeks from reflecting unwanted light to the outside, it is known to associate a mask with the lamp to prevent light from the source reaching said cheeks; it is also known that the cheeks can be coated in a light-absorbing substance such as matt black paint, however that solution can give rise to problems of appearance.
It is also known to design the cheeks so as to prevent them giving rise to radiation that could dazzle the drivers of on-coming vehicles, or so as to enable them to recover the radiation emitted by said source towards said cheeks in a manner that is of use, in particular for the purpose of returning said radiation towards the source.
It sometimes also happens that the mirror of a headlight has side cheeks, particularly if the shape of the mirror is elongate in the vertical direction, even though that kind of headlight has not been much developed since such a vertically elongate shape is not suited to generating a light beam having satisfactory photometric characteristics, and in particular small thickness.
In that case also, in order to ensure that the side cheeks do not reflect unwanted light out from the vehicle, it is necessary to provide means that use solutions based on those known for headlights that are horizontally elongate, and in any event the light flux emitted by the source to the cheeks is lost.
To improve the light efficiency of such a headlight, attempts have already been made to make a headlight whose mirror is defined by side cheeks and in which the cheeks are suitable for reflecting the light from the source so that it can contribute to the light beam.
However, in that case the cheeks have been plane or incapable of properly positioning the images of the source in the beam. It has been more a question of diluting light over the entire field in front of the vehicle, and it has not been shown that that contributes to visual comfort.
Document FR-A-2 639 295 discloses a headlight whose mirror possesses two side cheeks in the form of parabolic cylinders designed to reflect the radiation coming from the source so as to generate portions of the beam that are highly deflected laterally.
Nevertheless, given that the back of the mirror in that case is a paraboloid of revolution focused in the vicinity of the source, it results that the back of the mirror generates a first beam portion that is highly concentrated on the axis of the road, and that the cheeks generate second and third beam portions that are highly offset laterally from the first beam portion, while leaving gaps that are essentially lacking in light between the first beam portion and the second and third beam portions. It is then essential to use a glass that has arrangements for making the beam uniform. However it can be feared that this task imparted to the glass is practically impossible to fulfill, given the large angular offset between the various beam portions upstream therefrom.
Finally, FR-A-2 639 294 discloses a headlight whose mirror possesses cheeks suitable for superposing wider beam portions on relatively narrow beam portions, but in which the wider beam portions contribute to the full lateral extent of the beam.
The cheeks thus contribute to reinforcing light on the axis of the road to the detriment of the quantity of light that is emitted towards the sides, whereas specifically the backs of modern reflectors are suitable for generating a quantity of light on the axis that is sufficient and on the contrary what is required is extra light towards the sides of the road.
An object of the present invention is to mitigate those limitations of the state of the art. The invention thus seeks to take advantage of the lateral cheeks of a headlight mirror so that they add very usefully to the beam generated by the back of the reflector, i.e. so that they improve the photometric qualities of the beam, while still being suitable for use with a glass that is smooth or that deflects very little, and without problems arising of uniformity within the beam. Another object of the invention is to take advantage of mirror side cheeks to reinforce the light towards the sides without excessively increasing the quantity of light on the axis.
Thus, the present invention provides a motor vehicle headlight comprising a light source co-operating with a mirror and a glass, the mirror having a back and at least one side cheek exposed to radiation from the source, the headlight being characterized in that at least one of the cheeks is suitable in at least one zone for reflecting light so as to extend laterally and with continuity the beam generated by the back of the mirror, substantially without reinforcing said beam on the road axis, and in that the glass is smooth or deflects to a very small extent only.
Preferred but non-limiting features of the headlight of the invention are as follows:
the cheek or at least one of the cheeks has a reflecting surface suitable for positioning all of the images of the light source so that they lie beneath a predetermined cutoff of the beam emitted by the headlight;
the images of the light source generated by the cheek or at least one of the cheeks have their top points essentially in alignment on said cutoff;
the source is elongate and extends substantially horizontally and transversely relative to the optical axis of the mirror, and the cheek or at least one of the cheeks has a vertical profile constituted by a top half-parabola and a bottom half-parabola whose focal lengths are different from each other and are such that the respective focal lines thereof pass in the vicinity of the end of the source close to the cheek and in the vicinity of the end of the source remote from the cheek;
the source is elongate and oriented essentially along the optical axis of the mirror, and the cheek or at least one of the cheeks has a profile such that a light beam emitted tangentially by the edge of the source is reflected in a plane that is essentially horizontal, each light beam emitted by the remainder of the source being reflected with an inclination that is downwards relative to said horizontal plane;
the cheek or at least one of the cheeks has a vertical profile of generally parabolic shape with a focal length that is such that the focal line of the cheek passes in the vicinity of the source;
the axis of said parabola is tilted downwards so as to ensure that the light generated by the cheek or by at least one of the cheeks is directed downwards;
the cheek presents a shape that is cylindrical;
the reflecting surface of the cheek or of at least one of the cheeks is constituted by a plurality of offset steps, said cheek having a vertical section that is generally in the form of a vertical line;
the back of the mirror presents a height that is greater than its width;
the or each cheek of the mirror is made separately from the back and is fitted to said back; and
the horizontal section of the or each cheek is inclined outwards relative to an optical axis of the back of the mirror.